Image pickup element, method of manufacturing image pickup element, and electronic apparatus

ABSTRACT

An image pickup element includes: a semiconductor substrate including a photoelectric conversion section for each pixel; a pixel separation groove provided in the semiconductor substrate; and a fixed charge film provided on a light-receiving surface side of the semiconductor substrate, wherein the fixed charge film includes a first insulating film and a second insulating film, the first insulating film being provided contiguously from the light-receiving surface to a wall surface and a bottom surface of the pixel separation groove, and the second insulating film being provided on a part of the first insulating film, the part corresponding to at least the light-receiving surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Priority PatentApplication JP2013-202123 filed Sep. 27, 2013, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an image pickup element having a fixedcharge film on a semiconductor substrate, a method of manufacturing suchan image pickup element, and an electronic apparatus including such animage pickup element.

In a solid-state image pickup device (an image pickup device) such as acharge coupled device (CCD) image sensor and a complementary metal oxidesemiconductor (CMOS) image sensor, a solid-state image pickup element(an image pickup element) including a photoelectric conversion sectionis disposed for each pixel. The photoelectric conversion section of theimage pickup element may be configured of, for example, a semiconductormaterial such as silicon (Si). On a surface of the photoelectricconversion section, crystal defects and dangling bonds are present dueto breaking of a crystal structure. The crystal defects and the danglingbonds lead to extinction, due to recombination of an electron-hole pairgenerated in the photoelectric conversion section, or lead to generationof a dark current.

For example, International Publication No. WO 2012/117931 discusses asolid-state image pickup device of a backside illumination type. In thissolid-state image pickup device, in order to suppress generation of adark current, an insulating film (a fixed charge film) having negativefixed charge on a light-receiving surface (a back surface) of a Sisubstrate is formed. In the Si substrate, a photodiode is embedded as aphotoelectric conversion section. On a Si surface where the fixed chargefilm is formed, an inversion layer is formed. A Si interface is pinnedby this inversion layer, which suppresses the generation of the darkcurrent.

Further, in the Si substrate, a groove may be provided between pixelsnext to each other, and optical color mixture may be suppressed byfilling this groove with an insulating film.

SUMMARY

In general, the above-described groove is formed by dry etching.However, the dry etching may cause crystal defects and dangling bonds ona surface of the Si substrate (in particular, a wall surface and abottom surface of the groove), which may lead to an increase ininterface state. Therefore, a dark current may be easily generated.

It is desirable to provide an image pickup element capable ofsuppressing generation of a dark current, a method of manufacturing suchan image pickup element, and an electronic apparatus including such animage pickup element.

According to an embodiment of the present technology, there is providedan image pickup element including: a semiconductor substrate including aphotoelectric conversion section for each pixel; a pixel separationgroove provided in the semiconductor substrate; and a fixed charge filmprovided on a light-receiving surface side of the semiconductorsubstrate, wherein the fixed charge film includes a first insulatingfilm and a second insulating film, the first insulating film beingprovided contiguously from the light-receiving surface to a wall surfaceand a bottom surface of the pixel separation groove, and the secondinsulating film being provided on a part of the first insulating film,the part corresponding to at least the light-receiving surface.

According to an embodiment of the present technology, there is provideda method of manufacturing an image pickup element, the method includingforming a fixed charge film on a light-receiving surface of asemiconductor substrate that includes a photoelectric conversion sectionfor each pixel and has a pixel separation groove, wherein the forming ofthe fixed charge film includes forming a first insulating film to beprovided contiguously from the light-receiving surface to a wall surfaceand a bottom surface of the pixel separation groove, and forming asecond insulating film to be provided on a part of the first insulatingfilm, the part corresponding to at least the light-receiving surface.

According to an embodiment of the present technology, there is providedan electronic apparatus provided with an image pickup element, the imagepickup element including: a semiconductor substrate including aphotoelectric conversion section for each pixel; a pixel separationgroove provided in the semiconductor substrate; and a fixed charge filmprovided on a light-receiving surface side of the semiconductorsubstrate, wherein the fixed charge film includes a first insulatingfilm and a second insulating film, the first insulating film beingprovided contiguously from the light-receiving surface to a wall surfaceand a bottom surface of the pixel separation groove, and the secondinsulating film being provided on a part of the first insulating film,the part corresponding to at least the light-receiving surface.

In the image pickup element, the method of manufacturing the imagepickup element, and the electronic apparatus according to theabove-described embodiments of the present technology, the fixed chargefilm formed on the light-receiving surface side of the semiconductorsubstrate is a laminated film including the first insulating film andthe second insulating film. The first insulating film is providedcontiguously from the light-receiving surface to the wall surface andthe bottom surface of the pixel separation groove. The second insulatingfilm is provided on the light-receiving surface. By thus configuring thefixed charge film using two kinds of insulating films formed indifferent regions, an interface state of a surface of the semiconductorsubstrate (specifically, the wall surface and the bottom surface of thepixel separation groove) improves.

In the image pickup element, the method of manufacturing the imagepickup element, and the electronic apparatus according to theabove-described embodiments of the present technology, the fixed chargefilm is formed on the light-receiving surface side of the semiconductorsubstrate, as a laminated film including two kinds of insulating films(the first insulating film and the second insulating film) formed indifferent regions. This improves the interface state of the wall surfaceand the bottom surface of the pixel separation groove formed in thesemiconductor substrate, thereby allowing generation of a dark currentto be suppressed.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated in andconstitute a part of this specification. The drawings illustrateembodiments and, together with the specification, serve to describe theprinciples of the technology.

FIG. 1 is a cross-sectional diagram of an image pickup element accordingto an embodiment of the present technology.

FIG. 2A is a cross-sectional diagram used to describe a method ofmanufacturing a fixed charge film of the image pickup elementillustrated in FIG. 1.

FIG. 2B is a cross-sectional diagram illustrating a process following aprocess in FIG. 2A.

FIG. 2C is a cross-sectional diagram illustrating an example of aconfiguration of the fixed charge film, together with a processfollowing the process in FIG. 2B.

FIG. 3A is a cross-sectional diagram used to describe another method ofmanufacturing the fixed charge film of the image pickup elementillustrated in FIG. 1.

FIG. 3B is a cross-sectional diagram illustrating a process following aprocess in FIG. 3A.

FIG. 3C is a cross-sectional diagram illustrating another configurationexample of the fixed charge film, together with a process following theprocess in FIG. 3B.

FIG. 4 is a cross-sectional diagram of an image pickup element accordingto a modification of the present disclosure.

FIG. 5 is a functional block diagram of a solid-state image pickupdevice according to an application example.

FIG. 6 is a functional block diagram of an electronic apparatusaccording to another application example.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described below indetail with reference to the drawings. It is to be noted that thedescription will be provided in the following order.

1. Embodiment (an example in which a fixed charge film has a multilayerstructure, and layers are formed using different manufacturing methods)2. Modification (an example in which a light-shielding film is providedalso in a pixel separation groove)3. Application examples (application examples to a solid-state imagepickup device and an electronic apparatus)

1. Embodiment

FIG. 1 illustrates a cross-sectional configuration of an image pickupelement (an image pickup element 10) according to an embodiment of thepresent technology. The image pickup element 10 may configure, forexample, one pixel (for example, a pixel P), in an image pickup device(an image pickup device 1) such as a CCD image sensor and a CMOS imagesensor (see FIG. 5). The image pickup element 10 may be of a backsideillumination type, and includes a light receiving section 20, a wiringlayer 30, and a condensing section 40. The light receiving section 20includes a photoelectric conversion section 22. The condensing section40 is provided on a light incident surface (a light-receiving surfaceS1) side of the light receiving section 20. The wiring layer 30 isprovided on a surface on a side opposite to the light incident surfaceside. The light receiving section 20 includes a semiconductor substrate21, a fixed charge film 23, and a protective film 24. The semiconductorsubstrate 21 has a groove (a pixel separation groove 21A), which isprovided on the light incident surface side and between the pixels P.The fixed charge film 23 and the protective film 24 are provided on anentire surface, which is on the light incident surface side, of thesemiconductor substrate 21. The image pickup element 10 of the presentembodiment partially has a laminated structure in which the fixed chargefilm 23 is formed of two kinds of insulating films (a first insulatingfilm 23A and a second insulating film 23B) that are formed in differentregions.

A configuration of the image pickup element 10 will be described below,in order of the light receiving section 20, the wiring layer 30, and thecondensing section 40.

(Light Receiving Section)

The light receiving section 20 includes the semiconductor substrate 21and the fixed charge film 23. In the semiconductor substrate 21, forexample, a photodiode may be embedded as the photoelectric conversionsection 22. The fixed charge film 23 is provided on a back surface (thelight incident surface, or the light-receiving surface S1) of thesemiconductor substrate 21.

The semiconductor substrate 21 may be configured of, for example, p-typesilicon (Si), and has the pixel separation groove 21A as describedabove. The pixel separation groove 21A is provided between the pixels Pon the light-receiving surface S1 side, to extend in a thicknessdirection (a Z direction) of the semiconductor substrate 21. A depth (aheight (h)) of the pixel separation groove 21A may only be a depthallowing suppression of crosstalk, and may be, for example, 0.25 μm ormore and 5 μm or less. A width (W) of the pixel separation groove 21Amay only be a width allowing suppression of crosstalk, and may be, forexample, 100 nm or more and 1,000 nm or less.

In proximity to the surface (a surface S2) of the semiconductorsubstrate 21, a transfer transistor is disposed. The transfer transistormay transfer, for example, signal charge generated in the photoelectricconversion section 22, to a vertical signal line Lsig (see FIG. 5). Agate electrode of the transfer transistor may be, for example, providedin the wiring layer 30. The signal charge may be either an electron or apositive hole generated by photoelectric conversion. Here, a case inwhich an electron is read out as the signal charge will be described asan example.

In proximity to the surface S2 of the semiconductor substrate 21, forexample, components such as a reset transistor, an amplifyingtransistor, and a select transistor may be provided together with theabove-described transfer transistor. Such transistors may each be, forexample, a metal oxide semiconductor field effect transistor (MOSEFT),and included in a circuit for each of the pixels P. Each of the circuitsmay have, for example, a three-transistor configuration including atransfer transistor, a reset transistor, and an amplifying transistor,or may have a four-transistor configuration including a selecttransistor in addition to these three transistors. The transistorsexcept the transfer transistor may also be shared by the pixels.

The photoelectric conversion section 22 (the photodiode) may be, forexample, an n-type semiconductor region, which is formed in thethickness direction (the Z direction) of the semiconductor substrate 21(here, a Si substrate), for each of the pixels P. The photoelectricconversion section 22 may be a pn-junction-type photodiode, with ap-type semiconductor region provided in proximity to a front surface anda back surface of the semiconductor substrate 21. It is to be notedthat, in the semiconductor substrate 21, a p-type semiconductor regionis also formed between the pixels P, and the above-described pixelseparation groove 21A is formed in this p-type semiconductor region.

The fixed charge film 23 has negative charge, and has a configuration inwhich the first insulating film 23A and the second insulating film 23Bare partially laminated (for example, see FIG. 2C). Specifically, thefirst insulating film 23A is provided on the entire back surface of thesemiconductor substrate 21, namely, provided on the light-receivingsurface S1 of the semiconductor substrate 21 as well as contiguouslyfrom a wall surface to a bottom surface of the pixel separation groove21A. It is to be noted that the first insulating film 23A includesmultiple layers (here, two layers (23A₁ and 23A₂)). The secondinsulating film 23B is provided on a region (the light-receiving surfaceS1), which excludes an inner wall (the wall surface and the bottomsurface) of the pixel separation groove 21A, of the semiconductorsubstrate 21. It is to be noted that the second insulating film 23B isformed contiguously from the light-receiving surface S1 to a part of thewall surface of the pixel separation groove 21A.

The first insulating film 23A may be formed by, for example, atomiclayer deposition (ALD) or metal organic chemical vapor deposition(MOCVD). The second insulating film 23B may be formed, for example, byphysical vapor deposition (PVD). The first insulating film 23A and thesecond insulating film 23B may be formed in any lamination order, if thefirst insulating film 23A is at least directly formed on thesemiconductor substrate 21. In the present embodiment, as illustrated inFIG. 2C, the fixed charge film 23 may have, for example, a configurationin which the first insulating film 23A₁, the second insulating film 23B,and the first insulating film 23A₂ are laminated in this order from thesemiconductor substrate 21 side. Alternatively, as illustrated in FIG.3C, the first insulating film 23A₁, the first insulating film 23A₂, andthe second insulating film 23B may be laminated in this order from thesemiconductor substrate 21 side.

The first insulating films 23A₁ and 23A₂ may each preferably have, forexample, a thickness of 1 nm or more 25 nm or less. The first insulatingfilm 23A (23A₁ and 23A₂) may be preferably formed to have an overallthickness of 2 nm or more and 100 nm or less. This makes it possible toimprove pinning performance of the semiconductor substrate 21 on thewall surface and the bottom surface of the pixel separation groove 21A.The second insulating film 23B may preferably have, for example, a filmthickness of 10 nm or more and 80 nm or less.

As a material of the fixed charge film 23 (23A and 23B), a highdielectric material having fixed charge may be preferably used. Specificexamples of the material may include hafnium oxide (HfO₂), zirconiumoxide (ZrO₂), aluminum oxide (Al₂O₃), titanium oxide (TiO₂), andtantalum oxide (Ta₂O₅). These oxides have been used for films such as agate insulating film of an insulated-gate field-effect-transistor andtherefore, a film formation method has been established. Hence, films ofthese oxides may be easily formed. In particular, using materials suchas HfO₂ (a refractive index of 2.05), Ta₂O₅ (a refractive index of2.16), and TiO₂ (a refractive index of 2.20) whose refractive index isrelatively low, adds an antireflection effect to the fixed charge film23. Other examples of the material may include rare earth element oxide.Specific examples of the rare earth element oxide may include lantern(La), praseodymium (Pr), cerium (Ce), neodymium (Nd), promethium (Pm),samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium(Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium(Lu), and yttrium (Y). It is to be noted that silicon (Si) may be addedto the above-described oxide to the extent of not impairing aninsulation property. Alternatively, other than the oxide, nitride andoxynitride such as hafnium nitride, aluminum nitride, hafniumoxynitride, and aluminum oxynitride may be used. Adding Si or Ni to thefixed charge film 23 improves heat resistance and capability of blockingion implantation to a Si interface and the Si substrate during theprocess.

The first insulating film 23A (23A₁ and 23A₂) and the second insulatingfilm 23B may be configured of the same material, but the materials ofthe first insulating film 23A and the second insulating film 23B may bedifferent. A manufacturing process may be simplified using the samematerial for the first insulating films 23A₁ and 23A₂ that use a commonmanufacturing method. Alternatively, the first insulating films 23A₁ and23A₂ as well as the second insulating film 23B may be formed usingdifferent materials. Preferable materials of each of the insulatingfilms 23A₁, 23A₂, and 23B may be as follows. First, examples of thepreferable material of the first insulating film 23A₁ may include HfO₂,ZrO₂, and Al₂O₃. Examples of the preferable material of the firstinsulating film 23A₂ may include HfO₂, ZrO₂, Al₂O₃, TiO₂, and Ta₂O₅.Examples of the preferable material of the second insulating film 23Bmay include HfO₂, ZrO₂, Al₂O₃, TiO₂, and Ta₂O₅. In particular, use of amaterial having a high refractive index for the second insulating film23B, which is formed to be thicker than the first insulating film 23A,makes it possible to efficiently obtain an antireflection effect, and toimprove sensitivity of the image pickup element 10, by increasing lightentering the photoelectric conversion section 22.

The protective film 24 is provided on the fixed charge film 23, and aback surface of the light receiving section 20 is flattened by fillingthe pixel separation groove 21A with the protective film 24. Theprotective film 24 may be configured of, for example, a single layerfilm of silicon nitride (Si₂N₃), silicon oxide (SiO₂), siliconoxynitride (SiON), and the like, or a laminated film of these materials.

(Wiring Layer)

The wiring layer 30 is provided in contact with the surface (the surfaceS2) of the semiconductor substrate 21. The wiring layer 30 includes aplurality of wirings 32 (for example, 32A, 32B, and 32C) in aninterlayer insulating film 31. The wiring layer 30 may be, for example,adhered to a supporting substrate 11 made of Si. The wiring layer 30 isdisposed between the supporting substrate 11 and the semiconductorsubstrate 21.

(Condensing Section)

The condensing section 40 is provided on the light-receiving surface S1side of the light receiving section 20, and has an on-chip lens 41 on alight incident side. The on-chip lens 41 is disposed, as an opticalfunctional layer, to face the photoelectric conversion section 22 ofeach of the pixels P. Between the light receiving section 20(specifically, the protective film 24) and the on-chip lens 41, aflattening film 43 and a color filter 44 are laminated in this orderfrom the light receiving section 20 side. Further, a light-shieldingfilm 42 is provided on the protective film 24 between the pixels P.

The on-chip lens 41 has a function of condensing light towards the lightreceiving section 20 (specifically, the photoelectric conversion section22 of the light receiving section 20). A lens diameter of the on-chiplens 41 is set at a value corresponding to the size of the pixel P andmay be, for example, 0.9 μm or more and 8 μm or less. Further, arefractive index of the on-chip lens 41 may be, for example, 1.5 or moreand 1.9 or less. Examples of a lens material may include an organicmaterial and a silicon oxide film (SiO₂).

The light-shielding film 42 may be provided between the pixels P,namely, for example, at a position, which corresponds to the pixelseparation groove 21A, of the protective film 24. The light-shieldingfilm 42 suppresses color mixture due to crosstalk of obliquely enteringlight between the adjacent pixels. Examples of a material of thelight-shielding film 42 may include tungsten (W), aluminum (Al), and analloy of Al and copper (Cu). The light-shielding film 42 may have, forexample, a film thickness of 20 nm or more and 5,000 nm or less.

The flattening film 43 may be configured of, for example, a single layerfilm of any of silicon nitride (Si₂N₃), silicon oxide (SiO₂), siliconoxynitride (SiON), and the like, or a laminated film of any of thesematerials.

The color filter 44 may be, for example, any of a red (R) filter, agreen (G) filter, a blue (B) filter, and a white filter (W), and may be,for example, provided for each of the pixels P. These color filters 44are provided in a regular color array (for example, a Bayer array). Inthe image pickup element 10, light receiving data of colorscorresponding to the color array is obtained by providing these colorfilters 44.

The image pickup element 10 as described above may be manufactured asfollows, for example.

(Manufacturing Method)

First, the semiconductor substrate 21 including various transistors andperipheral circuits are formed. For the semiconductor substrate 21, forexample, a Si substrate may be used. In proximity to the surface (thesurface S2) of the Si substrate, the transistors such as the transfertransistor and the peripheral circuits such as a logic circuit areformed. Next, an impurity semiconductor region is formed by ionimplantation to the semiconductor substrate 21. Specifically, an n-typesemiconductor region (the photoelectric conversion section 22) is formedat a position corresponding to each of the pixels P, and a p-typesemiconductor region is formed between the pixels P. Subsequently, thepixel separation groove 21A may be formed at a predetermined position ofthe light-receiving surface S1 of the semiconductor substrate 21,specifically, in the p-type semiconductor region provided between thepixels P. The pixel separation groove 21A may be formed by, for example,dry etching, to have a depth (h) of 1 nm, for example.

Next, the fixed charge film 23 is formed on the light-receiving surfaceS1 side of the semiconductor substrate 21. Specifically, at first, asillustrated in FIG. 2A, the first insulating film 23A₁ may be formed by,for example, ALD or MOCVD. The first insulating film 23A₁ iscontiguously provided on the light-receiving surface S1 of thesemiconductor substrate 21 as well as from a wall surface to a bottomsurface of the pixel separation groove 21A. When ALD is used, the firstinsulating film 23A₁ may be formed based on, for example, suchconditions that a substrate temperature is 200° C. to 500° C., a flowquantity of a precursor is 10 sccm to 500 sccm, an irradiation time ofthe precursor is 1 second to 15 seconds, and a flow quantity of ozone(O₃) is 5 sccm to 50 sccm. When MOCVD is used, the first insulating film23A₁ may be formed, for example, using a substrate temperature of 100°C. to 600° C. It is to be noted that, when the Si substrate is used asthe semiconductor substrate 21 and the first insulating film 23A₁ isformed on the Si substrate by using ALD, a silicon oxide film reducingan interface state and having a thickness of about 1 nm is allowed to beconcurrently formed on the surface of the Si substrate.

Next, as illustrated in FIG. 2B, the second insulating film 23B may beformed on the first insulating film 23A₁, by using, for example, PVD.Conditions for this formation may be, for example, a pressure of 0.01 Pato 50 Pa, power of 500 W to 2,000 W, an Ar flow quantity of 5 sccm to 50sccm, and an oxygen (O₂) flow quantity of 5 sccm to 50 sccm. It is to benoted that, by a shadowing effect, the second insulating film 23B formedby PVD is formed only on the light-receiving surface S1 of thesemiconductor substrate 21 and on a part of the wall surface, which iscontiguous to the light-receiving surface S1, of the pixel separationgroove 21A. The second insulating film 23B is not formed in inside (mostpart of the wall surface and the bottom surface) of the pixel separationgroove 21A.

Next, as illustrated in FIG. 2C, the first insulating film 23A₂ may beformed on the second insulating film 23B and the first insulating film23A₁ by using, for example, ALD or MOCVD. The first insulating film 23A₁covers the wall surface and the bottom surface of the pixel separationgroove 21A. Conditions in ALD and MOCVD are similar to those describedabove. The fixed charge film 23 is thus formed.

As described above, after the first insulating film 23A₁ is formed onthe entire back surface of the semiconductor substrate 21 by ALD orMOCVD, the second insulating film 23B is formed on the light-receivingsurface S1 side of the first insulating film 23A₁ by PVD. The fixedcharge film (23A₁, 23B, and 23A₂) having an antireflection function isallowed to be formed on the surface part of the semiconductor substrate21 without degrading interfacial quality, and at the same time, thefixed charge film (23A₁ and 23A₂) improving the interface state isallowed to be formed in the groove.

It is to be noted that, as described above, the fixed charge film 23 maybe formed in film formation order other than the lamination orderillustrated in FIGS. 2A to 2C. Specifically, for example, the fixedcharge film 23 may be formed as illustrated in FIGS. 3A to 3C. First,the first insulating film 23A₁ is formed in a region from thelight-receiving surface S1 of the semiconductor substrate 21 to the wallsurface and the bottom surface of the pixel separation groove 21A byusing ALD or MOCVD in a manner similar to that in the above-describedmanufacturing process. Subsequently, the first insulating film 23A₂ isformed using ALD or MOCVD again. The second insulating film 23B is thenformed by PVD. In this way, if at least the insulating film is directlyformed on the back surface of the semiconductor substrate 21 by ALD orMOCVD that is less likely to damage a film-formed surface, anymanufacturing method may be adopted for an insulating film to besubsequently laminated.

Next, as the protective film 24, for example, a SiO₂ film may be formedon the fixed charge film 23 on the light-receiving surface S1 by using,for example, ALD or chemical vapor deposition (CVD). The pixelseparation groove 21A is filled with the SiO₂ film. Subsequently, forexample, a W film may be formed on the protective film 24 by using, forexample, sputtering or CVD, and then patterned by photolithography sothat the light-shielding film 42 is formed. Next, the flattening film 43is formed on the protective film 24 and the light-shielding film 42.Subsequently, for example, the color filter 44 in the Bayer array andthe on-chip lens 41 may be formed in this order on the flattening film43. The image pickup element 10 may be thus obtained.

(Operation of Image Pickup Element)

In the image pickup element 10 as described above, signal charge (here,an electron) may be obtained in the pixel P of the image pickup deviceas follows, for example. Upon entering the image pickup element 10through the on-chip lens 41, light L passes through the color filter 44and the like and then is detected (absorbed) by the photoelectricconversion section 22 in each of the pixels P, so that red, green, orblue color light is photoelectrically converted. Of an electron-holepair generated in the photoelectric conversion section 22, the electronmoves to the semiconductor substrate 21 (for example, the n-typesemiconductor region in the Si substrate) to be stored, while thepositive hole moves to the p-type region to be discharged.

(Functions and Effects)

As described earlier, in an image pickup element having a photoelectricconversion section configured of, for example, a semiconductor materialsuch as Si, a dark current may be easily generated due to crystaldefects and dangling bonds present on a surface of the photoelectricconversion section. The dark current may be suppressed by forming aninsulating film (a fixed charge film) having fixed charge, on a surfaceof a semiconductor substrate.

Further, in an image pickup element, optical color mixture may besuppressed by providing a groove between pixels of a semiconductorsubstrate and filling this groove with an insulating film. However, ingeneral, this groove is formed by dry etching and therefore, crystaldefects as well as an interface state are easily formed on a surface ofthe semiconductor substrate due to damage caused by the dry etching.Therefore, although the optical color mixture may be suppressed, thedark current may be easily generated.

The dark current generated in the groove may be suppressed by formingthe above-described fixed charge film on a wall surface and a bottomsurface of the groove. Further, an insulating film producing both adark-current suppression effect and an antireflection effect may beachieved using, for example, an insulating material having a refractiveindex of 2 or more as a material of the fixed charge film, and forming afilm of this material over the entire back surface including the groove.However, there has been the following issue for the fixed charge film.In general, PVD whose deposition rate is high is selected in view ofproducibility. However, PVD damages a film formation region, namely,here, the entire back surface of the semiconductor substrate includingthe groove, thereby degrading interfacial quality. In particular, a darkcurrent is more easily generated at the surface (the wall surface andthe bottom surface) of the groove, the surface being damaged by the dryetching used in forming the groove.

In contrast, in the image pickup element 10 and the method ofmanufacturing the same according to the present embodiment, the fixedcharge film 23 is a laminated film (including the first insulating film23A and the second insulating film 23B), and the layers thereof areformed using different methods. Specifically, at first, the firstinsulating film 23A₁ is formed using ALD or MOCVD on the semiconductorsubstrate 21 and then, the second insulating film 23B is formed usingPVD. Subsequently, the first insulating film 23A₂ is formed using ALD orMOCVD. When the formation of the film (the first insulating film 23A₁)by ALD or MOCVD is performed before the film formation by PVD asdescribed above, it is possible to prevent damage to the film formationsurface by PVD. This is due to properties of the first insulating film23A₁ formed by ALD or MOCVD.

When film formation is performed using ALD or MOCVD, a more minute filmwith a high degree of crystallization is formed. For this reason, thefirst insulating film 23A₁ acts as a protective film of thesemiconductor substrate 21, which reduces damage to the surface of thesemiconductor substrate 21 in forming the second insulating film 23B byPVD. Therefore, it is possible to improve the interfacial quality of thelight-receiving surface S1. In addition, it is possible to suppressdeterioration in unpinning that occurs due to physical damage to thewall surface and the bottom surface of the pixel separation groove 21Ain forming the pixel separation groove 21A or impurity inactivation byion irradiation. It is to be noted that a lower limit, which isnecessary for reduction of damage to the surface of the semiconductorsubstrate 21 by PVD, of the film thickness of the first insulating film23A₁ may be preferably 1 nm or more, and a upper limit may be preferably25 nm or less in view of a film formation time.

In addition, the first insulating films 23A₁ and 23A₂ are formed, usingALD or MOCVD, on the entire surface (the light-receiving surface S1 aswell as the wall surface and the bottom surface of the pixel separationgroove 21A) on the light incident surface side of the semiconductorsubstrate 21. Moreover, the second insulating film 23B is formed, usingPVD, on the light-receiving surface S1 and the part of the wall surface,which is contiguous to the light-receiving surface S1, of the pixelseparation groove 21A by the shadowing effect to be described below. Theshadowing effect in the second insulating film 23B depends on the depth(h) of the pixel separation groove 21A. The deeper the depth (h) is, thegreater the shadowing effect is, so that film formation on the wallsurface of the pixel separation groove 21A is suppressed. The depth (h)allowing suppression of the film formation on the wall surface may bepreferably 1 μm or more. When the depth (h) is less than 1 μm, a grooveshape may be desirably an overhang type.

As described above, in the present embodiment, the fixed charge film 23,which is formed on the light-receiving surface side of the semiconductorsubstrate 21 including the photoelectric conversion section 22, isformed as a laminated film including two kinds of different insulatingfilms (the first insulating film 23A and the second insulating film 23B)formed in different regions. Specifically, the first insulating film 23Ais formed on the entire surface (the light-receiving surface S1 as wellas the wall surface and the bottom surface of the pixel separationgroove 21A) on the light incident surface side of the semiconductorsubstrate 21 by using ALD or MOCVD. Further, the second insulating film23B is formed on the light-receiving surface S1 by using PVD. Inparticular, the second insulating film 23B is formed after the firstinsulating film 23A is formed and therefore, it is possible to form afixed charge film without damaging the surface of the semiconductorsubstrate 21. In other words, it is possible to provide an image pickupdevice in which the interface state of the surface (the light-receivingsurface S1 as well as the wall surface and the bottom surface of thepixel separation groove 21A) of the semiconductor substrate 21 isimproved and generation of a dark current is suppressed.

Further, the lamination order of the first insulating film 23A₂ and thesecond insulating film 23B after the first insulating film 23A₁ isformed on the semiconductor substrate 21 is not limited in particular.However, it is possible to prevent entrance of impurities such as oxygenand hydrogen into the semiconductor substrate 21, by forming the firstinsulating film 23A₂ after the second insulating film 23B is formed asillustrated in FIGS. 2A to 2C. This makes it possible to further improvethe interface state and pinning performance on the light-receivingsurface S1.

Furthermore, as compared with ALD and MOCVD, PVD provides a highdeposition rate and therefore, it is possible to form a film that isthick to some extent in a relatively short time by PVD. Therefore, byforming the second insulating film 23B using a material having arelatively high refractive index, antireflection performance of thefixed charge film 23 for obliquely entering light is improved, whichallows suppression of color mixture in the photoelectric conversionsection 22.

It is to be noted that, in the present embodiment, the fixed charge film23 is configured such that the first insulating film 23A includes twolayers and the second insulating film 23B includes one layer, but thesefilms may each include two layers, or three more layers.

2. Modification

FIG. 4 illustrates a cross-sectional configuration of an image pickupelement (an image pickup element 10A) according to a modification of theabove-described embodiment. The image pickup element 10A is of thebackside illumination type and has a structure having the plurality ofpixels P two-dimensionally arranged, in a manner similar to that of theabove-described embodiment. In the light receiving section 20 of theimage pickup element 10A, the pixel separation groove 21A is providedbetween the pixels P of the semiconductor substrate 21 in a mannersimilar to that of the above-described embodiment. The fixed charge film23 is formed on the light-receiving surface S1 of the semiconductorsubstrate 21 as well as the wall surface and the bottom surface of thepixel separation groove 21A, and the protective film 24 is formed on thefixed charge film 23. In a condensing section 50, in a manner similar tothat in the above-described embodiment, a flattening film 53, alight-shielding film 52, and a color filter 54 are laminated between thelight receiving section 20 and an on-chip lens 51. In the image pickupelement 10A of the present modification, the light-shielding film 52 isextended inside the pixel separation groove 21A, which is different fromthe above-described embodiment. Except this point, the image pickupelement 10A has a configuration similar to that of the image pickupelement 10, and has similar functions and effects as well.

In this way, in the present modification, the light-shielding film 52 isembedded in the pixel separation groove 21A of the light receivingsection 20. Therefore, it is possible to further suppress color mixturedue to obliquely entering light in the photoelectric conversion section22.

3. Application Examples

FIG. 5 illustrates an overall configuration of a solid-state imagepickup device (the image pickup device 1) in which any of the imagepickup elements (the image pickup elements 10 and 10A) of theabove-described embodiment and modification is used for each pixel. Theimage pickup device 1 may be a CMOS image sensor, and includes a pixelsection 1 a serving as an image pickup area, in a central part on thesemiconductor substrate 21. In a peripheral region of the pixel section1 a, for example, a peripheral circuit section 130 including a rowscanning section 131, a system control section 132, a horizontalselection section 133, and a column scanning section 134 may beprovided.

The pixel section 1 a may include, for example, a plurality of unitpixels P (each equivalent to the image pickup element 10 or 10A)two-dimensionally arranged in rows and columns. To the unit pixel P, forexample, a pixel driving line Lread (specifically, a row selecting lineand a reset control line) may be wired for each pixel row, and thevertical signal line Lsig may be wired for each pixel column. The pixeldriving line Lread transmits a drive signal for signal reading from apixel, and has one end connected to an output terminal of the rowscanning section 131, the output terminal corresponding to each row.

The row scanning section 131 includes components such as a shiftregister and an address decoder. The row scanning section 131 may be,for example, a pixel driving section that drives the pixels P of thepixel section 1 a row by row. A signal outputted from each of the pixelsP in the pixel row selected by the row scanning section 131 is suppliedto the horizontal selection section 133 through each of the verticalsignal lines Lsig. The horizontal selection section 133 may beconfigured of, for example, components such as an amplifier and ahorizontal selection switch provided for each of the vertical signallines Lsig.

The column scanning section 134 includes components such as a shiftregister and an address decoder, and drives the horizontal selectionswitches of the respective horizontal selection sections 133 whilesequentially scanning these horizontal selection switches. By thisselective scanning of the column scanning section 134, a signal of eachof the pixels P transmitted through each of the vertical signal linesLsig is sequentially outputted to a horizontal signal line 135, and thentransmitted to the outside of the semiconductor substrate 21 through thehorizontal signal line 135.

A circuit portion including the row scanning section 131, the horizontalselection section 133, the column scanning section 134, and thehorizontal signal line 135 may be directly formed on the semiconductorsubstrate 21, or may be disposed in an external control IC. It ispossible to provide this circuit portion in other substrate connected bya cable or the like.

The system control section 132 receives a clock provided from outsidethe semiconductor substrate 21 as well as data commanding an operationmode, and outputs inside information of the image pickup device 1. Inaddition, the system control section 132 may include, for example, atiming generator that generates various timing signals. The systemcontrol section 132 may control driving of the peripheral circuits suchas the row scanning section 131, the horizontal selection section 133,and the column scanning section 134, based on the various timing signalsgenerated by the timing generator.

The image pickup device 1 as described above is applicable to all typesof electronic apparatuses having an image pickup function. Examples ofthe electronic apparatuses may include camera systems such as digitalstill cameras and video cameras, as well as mobile phones. As anexample, FIG. 6 illustrates a schematic configuration of a camera (anelectronic apparatus 2). The electronic apparatus 2 may be, for example,a video camera capable of shooting a still image or a moving image. Theelectronic apparatus 2 may include an image pickup device (the imagepickup device 1), an optical system (an optical lens) 310, a shutterunit 311, a signal processing section 312, and a drive section 313.

The optical system 310 guides image light (incident light) from asubject to the pixel section 1 a of the image pickup device 1. Theoptical system 310 may include a plurality of optical lenses. Theshutter unit 311 controls an optical irradiation period and a shieldingperiod for the image pickup device 1. The drive section 313 controlsshutter operation of the shutter unit 311 and transfer operation of theimage pickup device 1. The signal processing section 312 performsvarious kinds of signal processing on a signal outputted from the imagepickup device 1. For example, an image signal Dout after the signalprocessing may be stored in a storage medium such as a memory, oroutputted to a unit such as a monitor.

Further, in the above-described embodiment and the like, theconfigurations of the image pickup element 10 and 10A of the backsideillumination type have been each taken as an example. However, thepresent technology is applicable to a front illumination type.

Furthermore, an inner lens (not illustrated) may be disposed between thelight receiving section 20 and the color filter 44 (or 54) of thecondensing section 40 (or 50).

Still furthermore, it is not necessary to provide all the components ofthe above-described embodiment and the like, and other component may beprovided.

It is possible to achieve at least the following configurations from theabove-described example embodiments of the disclosure.

(1) An image pickup element including:

-   -   a semiconductor substrate including a photoelectric conversion        section for each pixel;    -   a pixel separation groove provided in the semiconductor        substrate; and    -   a fixed charge film provided on a light-receiving surface side        of the semiconductor substrate,    -   wherein the fixed charge film includes a first insulating film        and a second insulating film, the first insulating film being        provided contiguously from the light-receiving surface to a wall        surface and a bottom surface of the pixel separation groove, and        the second insulating film being provided on a part of the first        insulating film, the part corresponding to at least a portion of        the light-receiving surface.        (2) The image pickup element according to (1), wherein the first        insulating film and the second insulating film are different in        number of layers.        (3) The image pickup element according to (1), wherein, in the        fixed charge film, the first insulating film, the second        insulating film, and the first insulating film are formed in        order from the semiconductor substrate side.        (4) The image pickup element according to (1), wherein, in the        fixed charge film, the first insulating film, the first        insulating film, and the second insulating film are formed in        order from the semiconductor substrate side.        (5) The image pickup element according to (1), wherein the        second insulating film is contiguous from the light-receiving        surface to a part of the wall surface of the pixel separation        groove.        (6) The image pickup element according to (1), wherein the first        insulating film and the second insulating film are each formed        of any one of hafnium oxide (HfO₂), zirconium oxide (ZrO₂),        aluminum oxide (Al₂O₃), titanium oxide (TiO₂), and tantalum        oxide (Ta₂O₅).        (7) The image pickup element according to (1), wherein the first        insulating and the second insulating film are made of a same        material.        (8) The image pickup element according to (7), wherein the        material is any one of hafnium oxide (HfO₂), zirconium oxide        (ZrO₂), aluminum oxide (Al₂O₃), titanium oxide (TiO₂), and        tantalum oxide (Ta₂O₅).        (9) The image pickup element according to (8), wherein the        material includes silicon.        (10) The image pickup element according to (1), further        comprising a protective film in the pixel separation groove.        (11) The image pickup element according to (10), wherein the        protective film is any one of silicon nitride (Si₂N₃), silicon        oxide (SiO₂) and silicon oxynitride (SiON).        (12) A method of manufacturing an image pickup element, the        method including    -   forming a fixed charge film on a light-receiving surface of a        semiconductor substrate that includes a photoelectric conversion        section for each pixel and has a pixel separation groove,    -   wherein the forming of the fixed charge film includes    -   forming a first insulating film to be provided contiguously from        the light-receiving surface to a wall surface and a bottom        surface of the pixel separation groove, and    -   forming a second insulating film to be provided on a part of the        first insulating film, the part corresponding to at least the        light-receiving surface.        (13) The method according to (12), wherein the first insulating        film is formed by atomic layer deposition or metal organic        chemical vapor deposition.        (14) The method according to (12), wherein the second insulating        film is formed by physical vapor deposition.        (15) An electronic apparatus provided with an image pickup        element, the image pickup element including:    -   a semiconductor substrate including a photoelectric conversion        section for each pixel;    -   a pixel separation groove provided in the semiconductor        substrate; and    -   a fixed charge film provided on a light-receiving surface side        of the semiconductor substrate,    -   wherein the fixed charge film includes a first insulating film        and a second insulating film, the first insulating film being        provided contiguously from the light-receiving surface to a wall        surface and a bottom surface of the pixel separation groove, and        the second insulating film being provided on a part of the first        insulating film, the part corresponding to at least the        light-receiving surface.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An image pickup element comprising: asemiconductor substrate including a photoelectric conversion section foreach pixel; a pixel separation groove provided in the semiconductorsubstrate; and a fixed charge film provided on a light-receiving surfaceside of the semiconductor substrate, wherein the fixed charge filmincludes a first insulating film and a second insulating film, the firstinsulating film being provided contiguously from the light-receivingsurface to a wall surface and a bottom surface of the pixel separationgroove, and the second insulating film being provided on a part of thefirst insulating film, the part corresponding to at least a portion ofthe light-receiving surface.
 2. The image pickup element according toclaim 1, wherein the first insulating film and the second insulatingfilm are different in number of layers.
 3. The image pickup elementaccording to claim 1, wherein, in the fixed charge film, the firstinsulating film, the second insulating film, and the first insulatingfilm are formed in order from the semiconductor substrate side.
 4. Theimage pickup element according to claim 1, wherein, in the fixed chargefilm, the first insulating film, the first insulating film, and thesecond insulating film are formed in order from the semiconductorsubstrate side.
 5. The image pickup element according to claim 1,wherein the second insulating film is contiguous from thelight-receiving surface to a part of the wall surface of the pixelseparation groove.
 6. The image pickup element according to claim 1,wherein the first insulating film and the second insulating film areeach formed of any one of hafnium oxide (HfO₂), zirconium oxide (ZrO₂),aluminum oxide (Al₂O₃), titanium oxide (TiO₂), and tantalum oxide(Ta₂O₅).
 7. The image pickup element according to claim 1, wherein thefirst insulating and the second insulating film are made of a samematerial.
 8. The image pickup element according to claim 7, wherein thematerial is any one of hafnium oxide (HfO₂), zirconium oxide (ZrO₂),aluminum oxide (Al₂O₃), titanium oxide (TiO₂), and tantalum oxide(Ta₂O₅).
 9. The image pickup element according to claim 8, wherein thematerial includes silicon.
 10. The image pickup element according toclaim 1, further comprising a protective film in the pixel separationgroove.
 11. The image pickup element according to claim 10, wherein theprotective film is any one of silicon nitride (Si₂N₃), silicon oxide(SiO₂) and silicon oxynitride (SiON).
 12. A method of manufacturing animage pickup element, the method comprising forming a fixed charge filmon a light-receiving surface of a semiconductor substrate that includesa photoelectric conversion section for each pixel and has a pixelseparation groove, wherein the forming of the fixed charge film includesforming a first insulating film to be provided contiguously from thelight-receiving surface to a wall surface and a bottom surface of thepixel separation groove, and forming a second insulating film to beprovided on a part of the first insulating film, the part correspondingto at least the light-receiving surface.
 13. The method according toclaim 12, wherein the first insulating film is formed by atomic layerdeposition or metal organic chemical vapor deposition.
 14. The methodaccording to claim 12, wherein the second insulating film is formed byphysical vapor deposition.
 15. An electronic apparatus provided with animage pickup element, the image pickup element comprising: asemiconductor substrate including a photoelectric conversion section foreach pixel; a pixel separation groove provided in the semiconductorsubstrate; and a fixed charge film provided on a light-receiving surfaceside of the semiconductor substrate, wherein the fixed charge filmincludes a first insulating film and a second insulating film, the firstinsulating film being provided contiguously from the light-receivingsurface to a wall surface and a bottom surface of the pixel separationgroove, and the second insulating film being provided on a part of thefirst insulating film, the part corresponding to at least thelight-receiving surface.